Prior art apparatus for heating and cooling chromatography columns employ ovens having insulated walls containing brackets on which chromatography columns are mounted. Conduits mounted on the holders supply and remove chromatography carriers and samples from the columns. Air in an oven is electrically heated and circulated by fans so that the heated air is directed to be incident on the columns, to heat the carriers and samples in the columns to an adequate temperature. To provide the required temperature for the carriers and samples in the column, the air frequently must be heated to 400.degree. C. to 500.degree. C.
When a chromatography operation has been completed it is desired to cool the columns as quickly as possible, as is typically done by introducing ambient outside room temperature air into the oven interior. In one prior art configuration, the ambient air is circulated away from the fan blades so it contacts plural baffles and walls inside of the oven and is then drawn back in through the fan by the fan blades.
While the prior art structure is generally satisfactory, there are certain disadvantages associated with it. Because the oven interior walls and baffles have a relatively large thermal inertia and mass, the ambient, cooling air introduced into the oven interior after the column is no longer operating is heated by these surfaces. This has a tendency to increase the time required to cool the oven interior and prolong the time between adjacent tests. Also, during the column operating mode, while the oven is closed and heating the columns, the air circulated by the fan contacts the oven interior walls and baffles, to transfer heat to these surfaces. This transfer of heat to the baffles and interior oven surfaces increases the temperature gradient within the oven. It is desirable to minimize temperature gradients within the oven during the heating operation so as to maintain the temperature of the chromatography columns constant.
In one prior art configuration, the air passes over the heater downstream of the mixing fan. In such an arrangement full advantage of the mixing action provided by the fan does not occur. In other configurations, the baffles and oven interior walls direct the air back to the fan inlet without the air ever being incident on the columns. Thus, this air adds to the thermal inertia of the oven, to increase the length of time required for cooling.
A problem with the prior art ovens is that during cooling the hot air can not be removed from the oven by exhaust fans located in proximity to the oven outlet. This is because the air to be removed from the oven during the cooling operation is so hot that it damages bearings of the fan. Therefore, it is desired to lower the thermal mass of the oven to as great as extent as possible so air removed from the oven during initial stages of the cooling operation has sufficient heat to damage fan components in close proximity to the outlet.
It is customary for chromatography column apparatus to include controllers, such as valves, for the flow of carrier and sample fluids into and out of the columns. The flow controllers are usually temperature sensitive, whereby it is desired to maintain the temperature of the flow controllers and a compartment or housing in which they are located substantially constant. It is also desired to locate the flow controller compartment and the oven in a single housing for the entire chromatography unit.
It is, accordingly, an object of the present invention to provide a new and improved chromatography column apparatus.
A further object of the invention is to provide a new and improved apparatus for heating and quickly cooling chromatography columns.
A further object of the invention is to provide a new and improved chromatography column heating and cooling apparatus wherein air directed from a heater in an oven toward the columns is incident on the columns prior to being incident on any interior baffles or walls of the oven.
A further object of the invention is to provide a new and improved chromatography column oven having low thermal mass so that heated air in the oven is quickly cooled.
Still a further object of the invention is to provide a chromatography column oven that can be quickly reused after an operating cycle has been completed.
A further object of the invention is to provide a new and improved gas chromatography column oven having a fan associated therewith, wherein the fan is positioned to suck air out of the oven.
A further object of the invention is to provide a new and improved chromatography column housing wherein the chromatography column oven and a container for flow control devices for the chromatography columns are cooled and maintained at relatively constant temperature by ambient outside air while the columns are in operation.